Clinical studies have defined a form of limited immunosuppression in patients with chronic schistosomiasis that develops progressively after initial infection. This supression is characterized by poor or absent lymphocyte proliferative responsiveness to parasite antigens and the progressive diminution of the granulamatous response schistosome eggs in vitro. These latter responses seem to be determined by the balance between OKT+ (helper) and OKT8+ (suppressor) T-lymphocytes in patients' peripheral blood monocular cells. In contrast to this T-lymphocyte functional decline, the levels of total and parasite specific IgE antibodies actually increase as schistosome infections become chronic. Qualitative analyses of these IgE antibodies (as well as of IgG antibody) are currently under way in an effort to define allergens and antigens that are stage- and species-specific and that could be of value immunodiagnostically.